Arc furnace electrode control apparatus



March 9, 1965 J. w. MOORE ARC FURNACE ELECTRODE CONTROL APPARATUS Filed sept. e, 1962 United States Patent C) 3,17 3,@52 ARC FURNACE ELECTRDE CNTRL APPARATUS .lames Wright Moore, Pittsburgh, Pa., assigner to Mc- Graw-Edison Company, li/iilwaulree, Wis., a corporation of Delaware Filed Sept. 6, 1962, der. No. 221,762 9 Claims. (Cl. S14- 61) This invention relates to arc furnaces and more particularly to apparatus controlling the position of arc furnace electrodes.

it is common practice in the production of high-grade steel to utilize polyphase electric arc furnaces having a plurality of electrodes and electrode positioning means associated with each of the electrodes. Current flows in such furnaces from the electrodes to the grounded furnace charge. That portion of the current path between the electrodes and the furnace charge comprises an arc, which provides the heat necessary for furnace operation. The electrode positioning means is adapted to position each of the electrodes in accordance with the length of its respective arc as indicated by the arc current and the are voltage so that when the arc current rises, indicating that the arc is too short, the electrode is raised and when the arc voltage rises, indicating that the arc is too long, the electrode is lowered.

lt is an object of the invention to provide new and improved iiuid control means for positioning the electrodes in an electric arc furnace.

Another object of the invention is to provide fluid control means for positioning the electrodes of an electric arc furnace wherein no positive drive means is required during an electrode lowering operation.

A further object of the invention is to provide twospeed electrode positioning means wherein the speed of electrode travel may be rapidly and conveniently changed therebetween.

These and other objects and advantages of the invention will become more apparent from the detailed description thereof taken with the accompanying drawing which schematically illustrates the electrode controlled mechanism according to the instant invention.

Referring now to the drawing in greater detail, an electric arc furnace l is shown to include a shell 2 containing a bath of molten furnace charge or melt 3 and three movable electrodes d, 5 and o positioned above the melt 3. The electrodes d, 5 and 6 are connected to three phase supply conductors '7, il and 9, respectively, which are, in turn, connected to a suitable source of three phase power (not shown). A iiuid motor lil is mechanically connected to each of the electrodes fi, 5 and ti by an electrode positioning arm l2 so that said electrodes may be raised and lowered in accordance with furnace conditions. Since identical operating mechanisms are provided for controlling the positioning of each of the electrodes 4, 5 and 6, only one of them is illustrated for the sake of brevity.

The hydraulic motor l@ includes a cylinder i3 and a piston ld coupled to the arm l2 and is actuated by the hydraulic control mechanism according to the instant invention which is shown to include an electrode condition sensing assembly i5, a hydraulic drive assembly le and a hydraulic control circuit lid.

The sensing assembly l5 includes a force balance device 19 coupled to the phase conductor 7 for sensing the voltage and current conditions therein and for providing a irst output signal when said voltage and current conditions indicate the necessity of an electrode raising operation and a second electrical signal when said conditions indicate the necessity for an electrode lowering operation. The hydraulic control circuit t3 is coupled to the force balance device i9 and is operable upon the receipt of the ICC first signal to couple the pressure side of the hydraulic motor 1li to the hydraulic drive mechanism 16. The hydraulic control circuit iti is also operative upon the receipt of the second signal from the force balance mechanism 19 to vent the pressure side of the hydraulic motor l@ to a sump Ztl.

rlC-he force balance device ll9 is of a conventional type and includes a pair of electromagnetic coils 22 and 24 having armatures 25 and 26, respectively, which are coupled to the opposite ends of a balance beam 28 which is pivotally mounted at its center on a fulcrum 3i). Beam 2S is composed of an electrical conductive material and carries a iirst electrical contact 3l adjacent the end coupled to plunger 2S and a second electrical contact 33 carried by the end connected to plunger 26. A rst stationary Contact 3d is disposed in spaced relation below the movable contact 3l and a second stationary contact 36 is disposed in spaced relation below the movable Contact 33.

A pair of springs 3d and 39 engage the beam 28 in the opposite sides of the fulcrurn 3d and are of equal strength so as to hold the beam 23 in a balanced position with the contacts 3l and 33 out of engagement with the contacts 34 and 36 respectively when the coils 22 and 2d are rie-energized. The beam 28 is connected by a condoctor 37 to a ground bus dd.

Electrode current is sensed by means of a current transformer di whose secondary is inductively coupled to phase conductor and a voltage proportional to this current is derived by means of an adjustable resistor 42 shunting the secondary of current transformer 4l. Coil 22 is connected across resistor 4t2 so that the voltage applied to the former will be proportional to the current flowing in phase conductor '7. A voltage proportional to the voltage across the electrode 4 is applied to coil Z4 by means of an adjustable resistor fill. Conductors 45 and do connect resistor d4 in series with coil 24 and the combination in parallel with the electrode 4. By the suitable adjustment of resistors i2 and 44, the voltage across the coil 22 and the coil 24 can be made equal when the predetermined desired voltage and current conditions exist in electrode 4, whereby the beam Z8 will remain in a neutral position with the contacts 3l and 33 out of engagement with the contacts 3d and 35.

The hydraulic driving mechanism le includes a pump 4S driven by a motor 5@ and having an inlet connected by a conduit 5l to the sump 2li and an outlet connected by a first conduit 52 to the pressure side of the piston i4 and by a second conduit 53 to the hydraulic control circuit Iri. A filter 54 and a shut-oilc valve 5S are disposed in conduit 5l. in addition, a cheek valve 57 and a pressure relief valve Eli are disposed in conduit 52 adjacent the outlet side of pump 43 While a shut-off valve dll is disposed in said conduit adjacent the cylinder 13, A bypass conduit 62 and a regulating valve 63 connect the output of pump le to the conduit 5l so that fine adjustments may be made in the fluid delivery rate to the piston i4.

Motor Sli is of the two speed, three phase AC type and is schematically illustrated to include a first set of input terminals 62 and a second set of input terminals 64 which are selectively engageable by a selector switch 65. When the selector switch engages the rst terminals 64, the motor 5d wil run at approximately twice the speed upon being energized Ias it will when the switch 65 engages the second terminals 62. As a result of this twospeed operation of motor 53 4and accordingly or" the pump 48, the output of the pump 48, and hence the upward velocity of the piston ld, may be correspondingly doubled.

The selector switch 65 is connectable lto a three phase alternating lcurrent supply system d'7 by a solenoid switch 63 operable `to close cont-acts di?. One side of the coil 'lil of the solenoid switch 68 is connected to a supply bus 7l while its other end is connected by conductor '72 to the iirst stationary contact 3do the force balance device 19. lt will be recalled that the conductive beam Z3 of the device t9 is connected to the ground bus du by a conductor 37.

The hydraulic contro-l circuit l includes three pressure responsive control valves 3b, 3l and 82 and each is provided with a solenoid operated pilot valve 35, 86 and S7, respectively. Control valve is disposed in conduit 53 and valve 8l is disposed in a conduit 83 which is connected at one end to .the conduit at its downstream side to the sump 2li'. lt can also be seen that valve 82 is connected by `conduit S9 in parallel with valve 6l.

Each of the valves 3d, 3l and E?. identical and eac-L respectively includes a Valve element Si?, @l wui is biased by a spring Mill, lul, and lill towards a seat llt?, lll, and M2. Each of the valves dll, "l d m @a alla of., also respectively includes a diaphragm ll, and l2?, which is connected to its associated avlve elements 9u, @l and 32 by stems ltl, l3l, and i312, respectively.

Each oi the solenoid operated pilot valves S5, and S7, respectively, includes solenoids 97 which are connected by stems 165', ide, and to valve ele ments llS, llo, ll, espectively. A sprng i255 biases valve element lit' of valve 35' away from its seat i3d while springs llSbT and 13?, respectively, ille and 117 toward their seats i3d and l The solenoid coil ldd oi valve S is connected by conductor i3d and manually operable witch 139 between the supply bus 'il and the groun i bus Coil ido of valve Si? is connected by conductor to the supply lr las e ements us l' and by conductor Al to the stationary contact 36 oi balance device i9 through a pressure switch A conductor 143 and a switch `llld connect the solenoid coil li-'7 of valve S7 in parallel with the coil M oi valve Se.

Pressure switch ld?. includes diaphragm. l5@ connected by a conduit ll to the pressure side of piston ll and is operative when said pressure is at a predetermined minimum value to hold contacts lSZ in a closed position against the action of a spring l5?, to thereby maintain the integrity of conductor lill.

A pilot supply conduit lS is connected to conduit 53 through a pressure reducinU restriction Conduit 157, iSd and l59 connect the pressure sides of diaphragm lZil, 121 and 122, respectively, to the pilot supply ccnduit 15S through their associated pilot valves.

Operation or the electrode control system will now be discussed. Assume that normal operation of the piston 14 is desired. ln this event, the selector switch d5 is positioned on the iirst terminals 62 and the switch ldis open. ln addition, the emergency shut-o switch E39 is open to maintain solenoid ldd die-energized so that spring lZS holds element M5 in open position whereby pilot duid is provided through conduit 157 to the pressure side of diaphragm 129 thereby holding element in open position. Assume further that the electrodes d, 5 mid 6 have been energized and initially lowered into proximity with the furnace charge 3 so that an are is struck between each and the grounded charge.

lf the voltage and current conditions in the electrode 4 are within the desired limits, the voltage across coils 22 and 2d will be substantially balanced so that they will exert equal downward pulls on their respective plungers 25 and 26 whereby the beam 23 will remain in a substantially horizontal position and the movable contacts 3l and 33 will be out of engagement with the stationary contacts 34 and 36, respectively. Under this condition of operation, solenoid 63 will remain open circuited so that contacts 69 will be open and motor Sti rie-energized. As a result, the pump 43 will be at rest and no iuid will be delivered to the pressure side oi pis-ton le so that there will be no upward movement of the electrode Also, downward movement of the piston lll, due to leal;-

"trough pump is prevented by the cheek In addition, because contacts 33 and 315 are out of engagement, solenoid 9d will also be cle-energizenl so that valve do will be closed and no pilot iluid will be provided to diaphragm lill whereby valve 3l will also be closed to prevent the discharge of iluid Afrom the pressure side of piston llt through conduits or S9. As a rcsult, the piston will be at rest.

hould the current in electrode d increase, indicating the electrode is too low, the voltage across coil 22 correspondingly increase. An increase in are ourrent also causes a decrease in arc voltage so that the voltage across coil 2.4i will decrease. As a result, the force of coil 22. acting on its plunger 25 will overcome the force of coil and on plunger' so that beam Z8 will pivot counterrcloeltwise to brin-g Contact 3l into engagement with the lixed contact and thereby complete an energizing circuit through the coil 7% of solenoid 68 traced from supply bus 7l to ground bus iii through conductors and 37 and the conductive beam 2S.

The energizing of coil fil closes contacts o9 to energize motor 5d which, in turn, drives the pump i3 and provides hydraulic pressure to piston lli which begins moving upwardly Ito raise the electrode Kl.

As electrode i rises, the arc eur ent will decrease and the are voltage will increase until the downward forces of coils 22 and will again be in balance to separate contacts 3l and 3d and rie-energize solenoid 63. This open circuits the motor 555 whereupon the electrode il will again come to rest.

lr", on the `otlI er hand, the are between the electrode 4 the furnace charge 3 becomes too long so that the arc voltage increases and the arc current decerases to values which exceed the desired limits, the voltage applied across coil 24 will exceed that applied across coil 22. As a result, the downward force exerted by coil 2liand its plu-nger 26 will exceed that exerted by coil Z2 on plunger 25 so that beam 2S will pivot clockwise to bring contact 33 into engagement with stationary Contact 36. This completes an energizing circuit to the coil ldd of solenoid from supply bus 7 1l through ground bus d@ traced throtwh conductors le@ and Ml, pressure switch M2, conductive beam 12S and the conductor 37. As a result, valve @d will open to provide pilot pressure to diaphragm lll whereupon valve -l will open. This completes a discharge path from the piston llto the sump Ztl through the conduits 53 and 88. As a result, the electrode d will begin lowering toward 'the charge 3. A tine adjustment of the rate of this lowering operation may be made by the setting of a regulating valve 33 in the conduit '13.

vAs the electrode d approaches the charge 3 the are will shorten to increase the are current and decrease the are voltage until a balance condition again exists between tne coils 22. and 2d. Upon the latter event, the balance beam 23 will resume a horizontal position moving contacts 33 out of engagement with the contacts 36. rfhe solenoid 96 is thereby dea-energized so that pilot valve 6 closes to disconnect the diaphragm 21 from the pilot supply conduit i551 As a result, leakage to the sump 2t? through a restricted conduit ll allows spring to overcome the diaphragm 1.2i and move element Ell onto its seat lll and thereby interrupt the further discharge oi the rate of this lowering operation may be made by the setting of a regulating valve 33 in the conduit 3d.

in the event that it is desired to run the electrode /l at twice normal speed, the switch 65 is placed on the second set of motor contacts 6d so that the motor Sil will drive the pump 4S at twice normal speed. As a result, the pump i8 will supply luid to the cylinder ld at twice the previous rate whereupon the electrode 4 will be raised at twice normal speed upon closing of contacts 3l and ln addition, in order for the electrode to lower at twice rated speed, switch ldd in conductor M3 is also closed, placing solenoid 97 in parallel with solenoid 96. As a result, the closing of contacts 33 and 36 will energize solenoid 97 as well as solenoid 96 so that both Valves 81 and 82 will be open to provide parallel discharge paths through conduits 88 and $9. This allows the piston 14 to move downwardly at twice normal speed.

Pressure valve 142 is a fail-safe device which prevents the energization of solenoids 96 and 97 and the consequent downward movement of electrode 4 in the event that the pressure beneath the piston 14 falls below a minimum desired Value.

If it is desired to prevent the automatic downward movement of electrode 4, switch 139 in conductor 138 is closed to energize solenoid 95. Upon this event, valve element 115 closes to remove pilot pressure from the diaphragm 120 whereupon valve 80 closes to prevent the iiow of discharge fluid between conduit 53 and conduits 88 or 89.

A pressure relief bypass valve 161 is connected in parallel with a rilter 162 connected in the leakage conduit d8 so that in the event iilter 162 becomes clogged, the lowering of the electrode d will not be prevented.

While only a single embodiment has been shown and described, it is not intended that the invention be limited thereto but only by the scope of the appended claims.

I claim:

l. Means for controlling an arc Ifurnace electrode in relation to a body of furnace charge, comprising a hydraulic motor, a reservoir of hydraulic iiuid, electroresponsive pump means having an output connected to said hydraulic motor and an input coupled to said reservoir, conduit means coupling said hydraulic motor to said reservoir, normally closed electroresponsive valve means in said conduit means `for preventing the discharge of said tiuid from said motor to said reservoir, c-ircuit means coupled to said electrode for producing a first output signal when the distance between said electrode and said charge becomes too small and for producing a second output signal when the distance between said electrode and said charge becomes too large, means coupled to said circuit means and operable upon the occurrence of said first signal to energize said electroresponsive pump means to drive said electrode upwardly and operable upon the occurrence of said second signal to energize said electroresponsive valve means so that said valve means is actuated to an open position to connect said iiuid motor to said sump and allow said electrode to lower, said last mentioned means being operative to de-energize said pump means or said valve means upon the disappearance of said first and second signals respectively.

2. A control for an arc furnace electrode comprising a hydraulic motor, a reservoir of hydraulic fluid, electrorcsponsive pump means having an output connected to said hydraulic motor and an input coupled to Said reservoir, conduit means coupling said hydraulic motor to said reservoir, normally closed electroresponsive valve means in said conduit means Afor preventing the discharge of said tluid from said motor to said reservoir, lirst circuit means coupled to said electrode for producing a rst electrical signal which is a function of the current in said electrode and a second circuit means coupled to said electrode for producing a second electrical signal which is a Ifunction of the voltage across said electrode, means coupled to said first and second circuit means for energizing said electroresponsive pump means to drive said electrode upwardly when said iirst and second signals have one predetermined relation and for energizing said electroresponsive valve means so that said valve means is actuated to an open position to connect said iiuid motor to said reservoir and allow said electrode to lower when said signals have another predetermined relation, said last mentioned means being operative to deenergize said pump means or said valve means when said signals have a relationship other than said one and another respectively.

3. Means for controlling an arc furnace electrode in relation to a body of furnace charge, comprising a uid motor, a reservoir of hydraulic tluid, pump means including electroresponsive driving means and having an output connected to the pressure side of said iluid motor and an input coupled to said reservoir, conduit means coupling the pressure side of said tiuid motor to said reservoir, normally closed valve means in said conduit means for preventing the discharge of said tluid from said motor, electroresponsive pilot means for actuating said valve means to an open position to connect said fluid motor to said sump and thereby initiate the lowering of said electrode, circuit means coupled to said electrode for producing a first electrical signal when the distance between said electrode and said charge is too short and a second electrical signal when the distance between said electrode and said charge is too long, signal responsive means connected to said circuit means and operative upon the occurrence of said rst signal to complete an energizing circuit to said electroresponsive driving means to acuate said pump means and to drive said electrode upwardly, said signal responsive means also being operative upon the occurrence of said second signal to complete an energizing circuit to said pilot means to actuate said valve means so that said uid motor is connected to said sump and said electrode is lowered, said signal responsive means being operative to interrupt said energizing circuits upon the respective disappearance of said signals.

4. A control for an arc furnace electrode comprising a hydraulic motor coupled to said electrode, a sump containing hydraulic iiuid, pump means including electroresponsive driving means and having an output connected to the pressure side of said hydraulic motor and an input coupled to said sump, conduit means coupling the pressure side of said hydraulic motor to said sump, normally closed valve means in said conduit means for preventing the discharge of said fluid from said motor, electroresponsive pilot means for actuating said valve means to an open position, first circuit means coupled to said electrode for producing a irst electrical signal which is a function of the current in said electrode and second circuit means coupled to said electrode for producing a second electrical signal which is a function of the voltage across said electrode, ratio means coupled to said first and second circuit means and operative when said rst and second signals have one predetermined ratio to complete an energizing circuit to said electroresponsive driving means to actuate said pump means and drive said electrode upwardly, said ratio means also being operative when said signals have another predetermined ratio to complete an energizing circuit to said pilot means to open said valve means so that said fluid motor is connected to said sump and said electrode is lowered, said ratio means being operative to open said energizing circuits to said electroresponsive driving means and to said pilot means when said signals have ratios dilerent than said one or another predetermined ratios respectively.

5. A control for an arc furnace electrode comprising a hydraulic motor coupled to said electrode, a sump containing hydraulic iiuid, pump means including electroresponsive driving means and having an output connected to the pressure side of said hydraulic motor and an input coupled to said sump, conduit means coupling the pressure side of said hydraulic motor to said sump, normally closed valve means in said conduit means for preventing the discharge of said fluid from said motor, electroresponsive pilot means for actuating said Valve means to an open position, iirst circuit means coupled to said electrode for producing a rst voltage signal which is a function of the current in said electrode and second circuit means coupled to said electrode for producing a second voltage signal which is a function of the voltage across said electrode, force balance means including a first coil connected to said first circuit means and a second coil connected to said second circuit snr/spes means, said force balance means also including a balance beam del'lectable when said first and second voltage signals have one predetermined ratio to complete an energizing circuit to said electroresponsive driving means to actuate-said pump means and to drive said electrode upwardly, said beam also being deliectable when said voltage signals have another predetermined ratio to complete an energizing circuit to said pilot means to actuate said valve means so that said liuid motor is connected to said sump and said electrode is lowered.

6. A- control for an arc furnace electrode comprising a hydraulic motor, a sump containing hydraulic huid, pump means including two-speed electroresponsive driving means and having an output connected to the pressure side of said hydraulic motor and an input coupled to said sump, first and second conduit means in parallel relation for coupling the pressure side of said hydraulic motor to said sump, irst and second normally closed valve means in said iirst and second conduit means respectively for preventing the discharge of said fluid from said motor, rst and second electroresponsive pilot means for actuating said first and second valve means to open positions respectively, first circuit means coupled to said electrode for producing a lirst electrical signal which is a function of the current in said electrode and second circuit means coupled to said electrode for producing a second electrical signal with a function of the voltage across said electrode, force balance means coupled to said lirst and second circuit means and being operative when said rst and second signals have one predetermined relation to complete an energizing circuit to said electroresponsive drivmeans to actuae said pump means to drive said electrode upwardly, said force balance means also being opertion so that said fluid motor is connected to said sumpA and said electrode is lowered, and manually operablel means for placing said second pilot means in parallel circuit relation with said first pilot means so that two parallel discharge paths are provided for a more rapid electrode lowering, said manually operable means also being operative to change the speed of said electroresponsive driving means for a more rapid electrode raising, said force balance means being operative to interrupt the energizing circuits to said driving means and said first pilot means when said signals have relationships other than said one or another respectively.

7. Means for controlling an arc furnace electrode in relation to a body of furnace charge, comprising a draulic motor, electroresponsive pump means having an output connected to said hydraulic motor, conduit means coupled to said hydraulic motor, normally closed valve means in said conduit means for preventing the discharge of hydraulic fluid from said motor, electroresponsive valve control means for opening said valve means, circuit means coupled to said electrode for producing a first electrical output signal when the distance between said electrode and said charge becomes too small and for producing a second electrical output signal when the distance between said electrode and said charge become too large, electrical signal responsive means coupled to said circuit means and to said pump means and to said valve control means, said Signal responsive means being operative upon the occurrence of said first signal to energize said electro responsive pump means to drive said electrode upwardly and upon the occurrence of said second signal to energize said electroresponsive valve control means to open said valve means and allow the discharge of hydraulic liuid from said motor so that said electrode is lowered, said signal esponsive means being operative to de-energize said pump means or said valve control means upon the disappearance of said r'irst and second signals, respectively.

8. Means for controlling an arc furnace electrode in relation to a body of furnace charge, comprising a fluid motor, pump means including electroresponsive driving means and having an output connected to the pressure side of said fluid motor, conduit means coupled to the pressure side of said fluid motor, normally closed valve means in said conduit means for preventing discharge of iuid from said motor, electroresponsive pilot means for actuating said valve means to an open position to vent said fluid motor and thereby initiate the lowering of said electrode, circuit means coupled to said electrode and to said driving means and said pilot means, said circuit means being operative when the distance between said electrode and said charge is too short for energizing said Vdriving means so that said electrode will be elevated,

said circuit means also being operative for energizing said pilot means when the distance between said electrode and said charge is toe long so that said valve means is opened and said electrode is lowered.

9. Means for controlling an arc furnace electrode in relation to a body of furnace charge, comprising a fluid motor, electroresponsive pump means having an output connected to the pressure side of tluid motor, conduit means coupled to the pressure side of said rltid motor,

'normally closed valve means and said conduit means for preventing discharge of hydraulic iuid from said motor, electroresponsive valve control means for actuating said valve means to an open position to vent said [luid motor and thereby initiate the lowering of said electrode, circuit means coupled to said electrode for producing a irst electrical signal when the distance between said electrode and said charge is too short and a second electrical signal when the distance between said electrode and said charge is too long, signal responsive means connected to said circuit means and operative upon the occurrence of said first signal to complete an energizing circuit to said electroresponsive pump means to drive said electrode up- Wardly, said signal responsive means also being operative upon the occurrence of said second signal to complete an energizing circuit to said electroresponsive valve control means to actuate said valve means so that said fluid motor is vented and said electrode is lowered, said signal responsive means being operative to interrupt said energizing circuits upon the respective disappearance of said signals.

References Cited by the Examiner UNITED STATES PATENTS 2,422,362 6/47 Moore 3 14-61 2,440,380 4/48 Payne 3 14-61 2,517,527 8/50 Moore 69-52 RCHARD M. WOOD, Primary Examiner.

SOSEPH V. TRUI-1E, Examiner. 

1. MEANS FOR CONTROLLING AN ARC FURNACE ELECTRODE IN RELATION TO A BODY OF FURNACE CHARGE, COMPRISING A BYDRAULIC MOTOR, A RESERVOIR OF HYDRAULIC FLUID, ELECTRORESPONSIVE PUMP MEANS HAVING AN OUTPUT CONNECTED TO SAID HYDRAULIC MOTOR AND AN INPUT COUPLED TO SAID RESERVOIR, CONDUIT MEANS COUPLING SAID HYDRAULIC MOTOR TO SAID RESERVOIR, NORMALLY CLOSED ELECTRORESPONSIVE VALVE MEANS IN SAID CONDUIT MEANS FOR PREVENTING THE DISCHARGE OF SAID FLUID FROM SAID MOTOR TO SAID RESERVOIR, CIRCUIT MEANS COUPLED TO SAID ELECTRODE FOR PRODUCING A FIRST OUPUT SIGNAL WHEN THE DISTANCE BETWEEN SAID ELECTRODE AND SAID CHARGE BECOMES TOO SMALL AND FOR PRODUCING A SECOND OUTPUT SIGNAL WHEN THE DISTANCE BETWEEN SAID ELECTRODE AND SAID CHARGE BECOMES TOO LARGE, MEANS COUPLED TO SAID CIRCUIT MEANS AND OPERABLE UPON THE OCCURRENCE OF SAID FIRST SIGNAL TO ENERGIZE SAID ELECTRORESPONSIVE PUMP MEANS TO DRIVE SAID ELECTRODE UPWARDLY AND OPERABLE UPON THE OCCURRENCE OF SAID SECOND SIGNAL TO ENERGIZE SAID ELECTRORESPONSIVE VALVE MEANS SO THAT SAID VALVE MEANS IS ACTUATED TO AN OPEN POSITION TO CONNECT SAID FLUID MOTOR TO SAID SUMP AND ALLOW SAID ELECTRODE TO LOWER, SAID LAST MENTIONED MEANS BEING OPERATIVE TO DE-ENERGIZE SAID PUMP MEANS OR SAID VALVE MEANS UPON THE DISSAPPEARANCE OF SAID FIRST AND SECOND SIGNALS RESPECTIVELY. 